Characteristics of Ulin Tree (Eusideroxylon zwageri) in the Wild

Eusideroxylon zwageri
Ulin or Bornean ironwood is a rare tree originating from Indonesia, Malaysia, Brunei, and the Philippines. In Indonesia, this tree grows in Sumatra, Java, Kalimantan, and Flores. Meanwhile, in Malaysia, the states of Sabah and Sarawak, in the Philippines, are in the Sulu Archipelago.

Ulin tree species are currently threatened with extinction due to habitat loss. The Indonesian government and the Sarawak state government officially prohibit the export of Ulin trees. Unfortunately, illegal smuggling continues and is a big problem. Also, overexploitation, lack of regeneration, and difficulty in cultivating Ulin contribute to the scarcity of this tree.

Ulin trees grow in primary and secondary forests ranging from lowlands to 600 m above sea level. The tree prefers dry, sandy, clay, to limestone rock. Ulin trees generally grow in groups between rivers and adjacent hills with an average annual rainfall of 2,500-4,000 mm.

One of the Ulin trees was discovered in 1993 in Kutai National Park, and it is included in the list of the largest plants in Indonesia. It is estimated that the tree is 1,000 years old, with a trunk diameter of 2.47 meters. However, its height had decreased from 30 meters to 20 meters after being struck by lightning.

It is different from the Ulin tree found in Sangkimah. The Ulin tree in Sangkimah, East Kalimantan has a trunk diameter of 2.25 meters and a height of about 45 meters.

Ulin is an extremely important tree and one of the world’s toughest producers of wood.


Characteristics of Ulin Leaf

Eusideroxylon zwageri Leaf
Source : ws

The leaves of the Ulin tree are simple, dark green, leathery, elliptical, 14-18 cm long, and 5-11 cm wide.


Characteristics of Ulin Flower

Eusideroxylon zwageri Flower
Source : Dr Kamarudin Mat-Salleh

Ulin flowers are yellow to greenish and even white.

Eusideroxylon zwageri Fruit
Source :

Characteristics of Ulin Trees in the Wild

Eusideroxylon zwageri Tree
Source :

Ulin trees are trees that have slow growth, only 0.05-0.5 cm in height per year. The average height of Ulin trees in the wild is over 50 meters with the lowest trunk diameter of 1-5-2 meters.

Each Ulin tree in its habitat can reach an age of 1,000 years or more.

Ulin seedlings need shade, while older trees need more sunlight.

Ulin trees are not suitable for large-scale plantations because of their very slow growth, besides the supply of seeds and seedlings is also inadequate (not freely available in the market).


The core of Ulin is light brown to bright yellow when cut, which gradually changes color to dark reddish, almost black, and the aroma of Ulin sap is very distinctive.

The most interesting thing about Ulin is its resistance to insects, bacteria, fungi, and borer because Ulin has anti-bacterial properties.

The durability of Ulin if placed indoors reaches more than 100 years, while if placed outside the house, on the ground, or for the hull of a boat, it can last for about 20 years.

Ulin is famous because it is often used as a material for making luxury furniture or furniture, therefore Ulin has a very high economic value.

INFO: For the manufacture of Ulin furniture, care and tools are needed because the wood is very hard, so special drill bits and saws are needed to cut, punch, carve and smooth it. Also, Ulin is also difficult to glue with synthetic resin.


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